At present, beacon lights are mainly evaluated in photometric laboratories, i.e. off-site, using test benches that have several axes of freedom in order to scan the entire solid angle of a light and to make the corresponding light intensity measurements. Such tests are performed using the principles and rules appropriate to sampling. They require lights and their bases to be dismantled. In addition, evaluation requires 100 to 200 light intensity measurement points to be acquired so as to be able to plot isocandela curves and mean values in standard ellipses.
That approach gives rise to numerous drawbacks, and in particular: it is expensive; it takes no account of lamp power supply or environmental parameters; the handling involved runs the risk of changing the state of internal and external dirt; and since evaluation is based on sampling, it is not exhaustive as recommended by the standards that are in force (OACI Annex 14). Such assurance can be obtained only by 100% inspection.
Thus, patent document GB-A-1 454 272 describes apparatus enabling the light intensity of runway beacon lights to be determined on-site. It comprises a vehicle 13 having an alignment of six optical detectors 1 disposed thereon, with the axis of each detector being at a different angle to the horizontal (in the range 1.degree. to 6.degree.). An inductor loop 6 serves to detect when the apparatus passes over a light and to determine the distance at which a light intensity measurement is to be performed.
However, such a single measurement implies firstly that said distance is measured with sufficient accuracy, and secondly that the sensors are in a complex geometrical disposition so as to make it possible to perform measurement simultaneously with the required speed and accuracy.
Any offset relative to the measurement axis or any drift in distance measurement will be interpreted as a wrongly functioning light and may give rise to interpretation error or even to no evaluation.
In addition, when the measurements performed relate to an organized light array, they represent only a low level of sampling, i.e. they provide six particular values taken from a set that has an infinite number of values, with light flux analysis being limited to a single vertical slice of the solid angle of emission. The representation obtained is thus discontinuous. Furthermore, the single information obtained per light is unsuitable for computer processing, and there is no possibility of recovering information in the event of an error or in the absence of acquisition, thus making it impossible to analyze the causes of attenuation if any.
It may also be observed that the probability of digitizing the maximum point in the emitted beam is reduced since detection takes place in a single plane only.